Air horns are commonly used as warning devices because they are capable of providing very loud and distinctive sounds that carry over large distances. For example, air horns are used in the mining and construction industry to provide warnings when blasting is about to take place and to signal all clear after such operations have concluded. In addition, air horns are used in emergency situations when an accident on a worksite has occurred. Some occupational health and safety regulations mandate the use of signaling in certain situations.
A very common kind of portable air horn apparatus consists of an air horn attached to a valve device that can be fitted to the neck of a compressed gas canister. The valve device includes a trigger that, when operated, allows compressed gas from the canister to operate the air horn. Devices of this kind are relatively inexpensive and lightweight and can generate sound at a high volume. However, gas canisters contain a finite amount of compressed gas that allows only a few uses before the canister has to be changed. Even worse, the valve devices tend to allow leakage of the gas from the canisters, thus further reducing the number of uses of the device before replacement of the canister is necessary. Gas leakage can also lead costly or dangerous situations in which an apparatus is unexpectedly found to be inoperative due to leakage and necessary warnings cannot be given, at least until a new canister can be obtained. The unreliability of apparatus of this kind makes it unsuitable for professional use.
There is consequently a need for more reliable and effective apparatus of this kind.